An MPEG-1 Audio Layer 3 (MP3) compressor is a program that takes audio files and compresses them down into MP3 files. Such a compressor normally uses masking so weaker, less memory-heavy sounds can be used in place of stronger ones, allowing the audio file to shrink in size. When an uncompressed audio file is put through an MP3 compressor, it normally will shrink by about 10 times. Benefits to using this type of program are that smaller audio files are easier to store, and downloading via the Internet is quicker. At the same time, this typically comes at the expense of lower-quality sound that can usually be fixed, but not always.

When it comes to hearing two similar pitches or frequencies, the human ear will rarely be able to tell the difference between them. An MP3 compressor takes advantage of this and converts most high-frequency sounds into slightly lower-frequency sounds. Lower frequencies typically require less memory, so the compressor is able to reduce how memory-heavy the file is by a considerable amount. This technique, known as masking, will not be noticed by most listeners, if they just listen to the MP3.

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An MP3 compressor usually is used on uncompressed audio files, though other compressed formats also can be converted into MP3s. On average, the compressor will shrink the uncompressed file down by 10 times; this means a 50 megabyte (MB) file will be from around 4.5 MB to 5 MB after conversion. The sound is usually smooth, and artifacts — or sound glitches — will rarely appear from the compression.

The major benefit of using a MP3 compressor is that the audio files are much smaller than before. The file is usually 10 times smaller, so around 10 times more songs can be saved on a computer or audio device. Downloading also is easier, because it will take much less time for a 5 MB file to download compared to an uncompressed 50 MB file.

While they are smaller, there usually is a problem with using an MP3 compressor, and that is lower quality. Masking is able to keep this at a minimum but, if people listen to the compressed and uncompressed files side by side, they normally will notice a slight difference. There are compression algorithms that limit the drop in quality with advanced masking; these files are typically somewhat larger in memory, but the algorithms also recognize and eliminate silent portions of the audio, so the file’s weight generally balances out.

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